1. Field of the Invention
This invention relates in part to improvements in methods and apparatuses for dynamic information storage or retrieval, and more particularly to improvements in methods and circuitry for positioning a transducer for writing or detecting data written onto a spinning data disk, and still more particularly to improvements in microactuator structures and methods for making same. This invention also relates in part to improvements in components used in microelectromechanical systems and methods for making same.
2. Relevant Background
Mass data storage devices include well known hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Many applications are still being developed. Applications for hard disk drives are increasing in number, and are expected to further increase in the future. Mass data storage devices may also include optical disks in which the optical properties of a spinning disk are locally varied to provide a reflectivity gradient that can be detected by a laser transducer head, or the like. Optical disks may be used, for example, to contain data, music, or other information.
In the construction of mass data storage devices, a data transducer, or head, is generally carried by an arm that is selectively radially positionable by a servo motor. Recently, micromotors, or microactuators, have been investigated to provide better, or more accurate, position control of the head.
In one design, a piezoelectric xe2x80x9cI-beamxe2x80x9d element has the actuator mounted on an arm or suspension element. The actuator may be co-located with the head on the end of a suspension to provide a fine positioning capability to the head. However, the piezoelectric element suffers several disadvantages. For example, voltages on the order of 30 volts are required for suitable operation. Such high voltages are undesirable in most hard disk drive applications. Also, the range of movement that can be achieved is on the order of only xc2x11 xcexcm. This may be enough with sufficiently high disk rotation velocities, but it is generally seen as a limitation of this system.
In another design, a microactuators that has been investigated has a microactuator element co-located with the head on the end of the arm. The microactuator may be rectangular in shape, with a platform portion to which the head is attached, and a frame portion to which the platform is tethered. The platform and frame are designed to allow the platform to freely move in only one direction in response to a current applied to associated coils. The movement of the platform causes fine radial movement of the head, for example, on the order of xc2x15 xcexcm, in an axis normal to the length of the arm.
Through the provision of fine head positioning, such as by the microactuators of the type described, the track density can be packed closer together since the head position can be more accurately controlled. Thus, the higher precision of head positioning can lead to a higher number of tracks per inch that can be created on the disk. Also, the speed of the motor can be increased, and the quality of the bearings can be decreased, since the head can be more accurately positioned.
From a three-dimensional perspective, when multiple disks are used with corresponding multiple heads, the ability to provide fine position control to individual heads of the stack of heads and disks enables each head to be individually positioned to tracks within its position control range. This is in contrast to structures that are required to track along the same paths as each of the other heads. This adds great flexibility and functionality to the drive that would not otherwise be available. Among other things, this would provide an ability to write to the disks with parallel data streams, greatly increasing its speed.
In the construction of microactuators in the past, one process that was used began with a silicon wafer about 24 mils thick. For example, a cross-section side view of a portion 10 of a microactuator is shown in FIG. 1. As can be seen, a nickel-iron structure 12 is formed on a silicon wafer substrate 14, on both sides of a gap 16. The gap 16 shown is the gap separating the tethered wafer structure 18 and the surrounding arm structure 20.
A dielectric material 22 is built up adjacent to the nickel-iron material 12, and copper coils 24 and connection wiring 26 surround a portion of the nickel-iron structure 12, encapsulated by the dielectric 22. The various structures are built up in layers by photolithographic, material deposition, lapping, and other known processes. These layers of dielectric, copper, and nickel-iron were built up on the wafer to form a sandwich of materials. The nickel-iron provided a necessary magnetic material, and the copper formed the coils to which a positioning current may be applied. Then the silicon wafer was lapped, sawed, or ground off to produce a microactuator which had a thickness on the order of about 100 xcexcm. Once this was done, however, due to the significantly differences of thermal coefficients of expansion of the various materials, the extremely thin resulting part was extremely vulnerable to warping or buckling. The various parts also tend to delaminate from the remaining wafer substrate, and made the production yield extremely small.
Limited capability of either molding or a photographic process, which is utilized to construct the high aspect ratio (height-to-width) layers of metal and dielectric material, are also important problems. The thickness of these material layers is a primary factor in generating the required amount of magnetic force in the micromotor, or microactuator. This force, in turn, drives the amount of travel of the platform in the motor. Large travel is a key market desire.
What is needed, therefore, is a microactuator structure and method for constructing it that results in a device that is not as susceptible to the stresses caused by the differences in the thermal coefficients of expansions of the various required materials.
Additionally, recent interest has been devoted to microelectromechanical systems (MEMS), for many varied applications, such as accelerometers, mirror positioning, and the like. In many MEMS control devices, a platform is suspended by a hinge or tether in a window in a larger yoke or base. However, the substrates upon which such structures are constructed are generally very thin, on the order of a few to a few hundred microns. Consequently, they suffer the same distortion problems as described above with respect to the mass data storage device positioning arms.
In light of the above, therefore, it is an object of the invention to provide a microactuator or micromotor device that is less susceptible to distortion or warping, due to differences in thermal expansion of the various parts used to realize the structure.
It is another object of the invention to provide improved methods for manufacturing microactuator or H micromotor devices, for use, for example, in mass data storage devices or microelectromechanical systems.
Thus, according to one aspect of the invention, a method for making a micromotor or microactuator is presented such that a symmetrical build up of material is allowed, thus reducing mechanical stress. More particularly, one layer of circuits is built on each side of the structure, thereby eliminating the need to stack complex patterns. Stacking one complex pattern on top of a similar pattern is difficult, because the surface, which is the base for subsequent layers, is not flat. The photolithography process that forms these patterns is not very forgiving to non-flat surfaces. Avoiding the stacked layers also allows thicker conductors to be considered for each circuit. Thicker circuits increase current carrying capacity, which is one of the key variables that increases the power of the micromotor.
According to another aspect of the invention, a method is presented to build a balanced micromotor by starting with a thin silicon wafer, plasma etching the desired pattern for the coil traces into the silicon and then plating copper or other electrically conductive metal into that pattern. NiFe metal is then built up on the two sides of the silicon, at the interface between the movable and non-movable segments of the device, and through the middle of the coil traces. This completes the material set required to form an electromagnetic field that is the source of the force driving the movement of the micromotor.
In yet another embodiment, a manufacturing method is presented which is similar to previous methods except that the sequential layers are added to both sides of the silicon wafer. This provides a balanced mechanical stress structure. This alternative utilizes a variation of the above-described method to form the electrical path to connect the bottom and top circuits. The silicon will be removed and an electrically conductive material, such as copper, will be deposited in the via. The layers of circuits for the motor coils and the NiFe are added in an alternating, sequential manner to the two sides of the silicon.
In still another embodiment, a piece-part manufacturing approach is presented. In this approach, two NiFe parts and dielectric and copper piece-parts are manufactured separately. This method allows the NiFe parts to be designed in a manner to maximize the thickness of the metal, which in turn increases the magnetic properties of the motor. The dielectric and copper coils piece-part may be a thin-film interconnect or some derivative of a standard flex circuit printed wiring board. These piece-parts may be tested individually, defective parts discarded, and only functional units assembled. This not only produces a mechanically balanced construction, but has lower cost due to non-sequential manufacturing steps. The dielectric and copper coils piece-part also provides the path for electrical connections to the movable platform and a relatively easy method for electrical connection off the microactuator and onto the hard disk drive system.
Thus, according to a broad aspect of the invention, a microactuator of the type having base and a platform hinged or tethered thereto is presented. The microactuator has first microactuator elements constructed on the base and second microactuator elements mounted on the opposite side of the base. The first microactuator elements are located substantially symmetrically on either side of a plane along a centerline of the substrate base so that warpage of the parts due to thermal expansion of the parts on each side of the plane cancel.
According to another broad aspect of the invention, a microactuator for use in a mass data storage device of the type having an arm that carries a transducer that is selectively positioned adjacent a spinning rotating disk is presented. The microactuator has a first portion carried by the arm and a second portion tethered in an aperture in the first portion to form a platform therewithin. First microactuator elements are mounted in the first portion, and second microactuator elements are mounted in the second portion so that movement of the platform moves a position of the transducer. The first microactuator elements are located substantially symmetrically on either side of a plane along a centerline of the first portion.
According to another broad aspect of the invention, a method is presented for manufacturing a microactuator structure. The method includes providing a substrate having first and second opposing sides, and alternatively and sequentially building up structure layers of the microactuator on the first and second sides.
According to yet another broad aspect of the invention, a method for manufacturing a microactuator structure is presented. The method includes providing a substrate having first and second opposing sides, and simultaneously building up structure layers of the microactuator on the first and second sides.